There is nothing wrong with offline multiplayer, indeed. But not having online mutliplayer as well is ridiculous, in my opionion. Maybe it's because I'm more of a PC player nowadays, but I think a good game should always have both options. I remember being disappointed because Rayman Origins had only offline coop - the sequel supports online play. Finally! But Nintendo? They don't seem to care. I remember Miyamoto's statement about not having online play in NSMB Wii saying it was because of the limitations of the console. Well, seems like it was just a lame excuse because this time they could have delivered.
Regarding the new things: It's obvious that when you show a new Mario game you show some new things. New power-ups and gameplay mechanics are mandatory. But I was never "blown-away" because someone showed a new powerup or a new level. The entire concept is what interests me.
And yes, a reviewer should play a game, score it and say if it's a must-have or not. But the thinking "you can't have an opinion on that if you haven't played it" doesn't work. Sometimes you can see a game is flawed or isn't your cup of tea. Sometimes it's obivous the game isn't a step forward. And I don't think you have to have played a game for that ability. There are always exceptions, of course, but with this game, I don't see it. I don't say it's a bad game. I know it's gonna be great. It's gonna have quality.
But in the end, it isn't the next leap in Mario jump'n'runs. If all you want is just another Mario game - it's fine. But not everyone thinks that way. And I doubt there will be millions buying a WiiU for a game you can basically play right now on your 3DS.